Signal Transduction Essay Example

Signal Transduction Essay Cells are not only the â€Å"smallest units of life† but they also depict â€Å"the best machineries in the world†. Cells not only work exceptionally well within their own systems but coordinate efficiently with other cells in order to ensure their survival. Reactivity, which refers to the living thing’s ability to respond to signals from the environment; enables the organism to react to various stimuli, either behaviorally or physiologically (The Characteristics of Life). Signals come in various forms such as changes in temperature, illumination, pressure and even intercellular chemical concentration. Other signals which take subtler forms are those which signal either cell division or cell differentiation. Protective responses are also carried out by most cells whenever foreign substances intrude the organism’s body. Such feats are only possible through signaling systems which are either intracellular or intercellular (The Cell Signaling Test) and are ge nerally referred to as signal transduction pathways.Signal transduction figures in information metabolism. Information metabolism refers to the cell’s reception, processing and consequent response to information from the environment (Signal Transduction Pathways: An Introduction to Information Metabolism). At the cellular level, signal transduction refers to the movement of signals from the outside to the inside of the cell. The process through which signal transduction occurs varies depending upon the nature of chemicals and their associated receptors. Signal movement can be as simple as those which involve the receptor molecules of the acetylcholine class or can be as complex as those which involve combinations of ligand – receptor interactions and several intracellular events. In the case of simple signal transduction, signals pass in or out of the cell through receptors which are mainly composed of channels. The process is effected out by ligand interaction through the form of small ion movements. These ion movements in turn result to changes in the cell’s electrical potential and consequently, to the propagation of the said signal along the cell (Mechanisms of Signal Transduction). Complex signal transduction, as mentioned before, does not only involve ligand interactions but also several intracellular events. These events include phosphorylations induced by the enzymes tyrosine kinases and/or serine/threonine kinases. Protein phosphorylations are specifically helpful in understanding the process of gene expression since they influence, to a large extent, enzymatic activities and protein conformations (Mechanisms of Signal Transduction).Pathways of signal transduction could therefore be depicted as molecular circuits. A pathway typically begins with the transfer of information from the environment towards the cell’s internal system. Nonpolar molecules (steroid hormones such as estrogen) could easily penetrate the cell membrane and could therefore, enter the cell. Once inside the cell, these molecules bind to proteins and interact with the cell’s DNA. The consequence of this interaction is that the molecules’ directly influence gene transcription. Other molecules, such as those which are too large or too polar, are not able to pass through the cell’s membrane. The information that these molecules carry must then be transmitted to the cell’s interior through another means. Such means is accomplished through the action of a membrane – associated receptor protein. A receptor of such type has often two domains: an extracellular and an intracellular domain. The former contains a binding site to which a ligand or a signal molecule is recognized. The interaction between the receptor and ligand consequently alters the receptor’s tertiary or quaternary structure as well its intracellular domain. Though such structural changes have been effected, the small number of receptor molecules in the cell membrane limits, or to a certain extent, hinders the yielding of an appropriate response. Ligands or primary messengers therefore, carry information which is transduced into forms which can either modify or influence the cell’s biochemistry.Second messengers comprise the next step in the transduction pathway. These messengers relay information from the receptor – ligand complex through changes in their concentration. Changes in concentration amplify the signal’s effect and influence, to a large extent, intracellular signal and response.   Protein phosphorylation is another means of information transfer. Responses are elicited by the activation of enzymes such as protein kinases. These enzymes transfer phosphoryl groups from ATP to certain protein residues such as serine, tyrosine and threonine through the process of phosphorylation. cAMP-dependent protein kinase as well as other protein kinases are links that transduce changes in the fre e second messenger concentration into alterations in protein covalent structures. These changes are less transient compared to secondary – messenger concentrations but the results of such process are reversible (Signal Transduction Pathways: An Introduction to Information Metabolism).Once the signal has been initiated and has been transduced to affect other cellular processes, it is equally important that the signal is terminated effectively. Signal termination is mostly carried out by the action of protein phosphatases. Whereas protein kinases are responsible for phosphorylation (Signal Transduction Pathways: An Introduction to Information Metabolism), protein phosphatases are responsible for dephosphorylation (Protein Phosphatases).   Dephosphorylation refers to the removal of a phosphate group (Dephosphorylation). The importance of this phase in the signal transduction pathway is clearly manifested when the process goes awry. If the effects of a previous signal are sti ll in effect, the cell could not respond to new and incoming signals. Cancers and uncontrolled cell growth are often the offshoot of the failure in this phase of the pathway (Signal Transduction Pathways: An Introduction to Information Metabolism).

Using If-Then-Else and Switch in Conditional Statements

Using If-Then-Else and Switch in Conditional Statements Conditional statements in a computer program support decisions based on a certain condition. If the condition is met, or true, a certain piece of code is executed. For example, you want to convert user-entered text to lowercase. Execute the code only if the user entered capitalized text. If not, you dont want to execute the code because it will lead to a runtime error. There are two main conditional statements used in Java:  the if-then and  if-then-else statements, and the switch statement. The If-Then and If-Then-Else Statements The most basic flow control statement in Java is if-then: if [something] is true, do [something]. This statement is a good choice for simple decisions. The basic structure of an if statement starts with the word if, followed by the statement to test, followed by curly braces that wrap the action to take if the statement is true. It looks like this: if (  statement  ) {// do something here....} This statement can also be extended to do something else if the condition is false: if (  statement  ) { // do something here...}else {// do something else...} For example, if you are determining whether someone is old enough to drive, you might have a statement that says if your age is 16 or older, you can drive; else, you cannot drive. int age 17;if age 16 {System.out.println(You can drive.);}else  {System.out.println(You are not old enough to drive.) There is no limit to the number of else statements you can add.   Conditional Operators In the example above, we used a single operator. These are the standard operators you can use: equal to: less than: more than: greater than or equal to: less than or equal to: In addition to these, there are four more operators used with conditional statements: and: not:!  or: ||is equal to:    For example, the driving age is considered to be from age 16 to age 85, in which case the AND operator can be used. else if ( age 16   age 85 ) This will return true only if both conditions are met. The operators NOT, OR, and IS EQUAL TO can be used in a similar way. The Switch Statement The switch statement provides an effective way to deal with a section of code that could branch in multiple directions based on a single variable. It does not support the conditional operators the if-then statement does, nor can it handle multiple variables. It is, however, a preferable choice when the condition will be met by a single variable because it can improve performance and is easier to maintain.   Heres an example: switch ( single_variable ) {case value://code_here;break;case value://code_here;break;default://set a default;} Note that you start with the switch, provide a single variable and then set out your choices using the term case. The keyword break completes each case of the switch statement. The default value is optional, but good practice. For example, this switch prints the lyric of the song  Twelve Days of Christmas  given a provided day. int day 5; String lyric ;  // empty string to hold the lyric switch (day) {case 1: lyric A partridge in a pear tree.;break;case 2:lyric 2 turtle doves;break;case 3:lyric 3 French hens;break;case 4:lyric 4 calling birds;break;case 5:lyric 5 gold rings;break;case 6:lyric 6 geese-a-laying;break;case 7:lyric 7 swans-a-swimming;break;case 8:lyric 8 maids-a-milking;break;case 9:lyric 9 ladies dancing;break;case 10:lyric 10 Lords-a-leaping;break;case 11:lyric 11 pipers piping;break;case 12:lyric 12 drummers drumming;break;default:lyric There are only 12 days.;break;}System.out.println(lyric); In this example, the value to test is an integer. Java SE 7 and later support a string object in the expression. For example:String day second;String lyric ;  // empty string to hold the lyric switch (day) {case first:lyric A partridge in a pear tree.;break;case second:lyric 2 turtle doves;break;case third:lyric 3 French hens;break;// etc.